1. Field of Invention
The invention relates to a filter medium and a method for producing the filter medium using a function member accommodated between two fiber layers.
2. Description of Related Art
As a filter for an internal combustion engine, for example, a filter of a sandwich structure in which activated carbon for absorbing fuel vapor is accommodated between nonwoven fabrics which filters air is used. FIG. 12 is an exploded perspective view showing a portion of a production process of a filter 100.
In producing the filter 100, a flat nonwoven fabric is first produced. Next, activated carbon is accommodated between two sheets of the nonwoven fabric, and the sheets of nonwoven fabric are press-formed into a corrugated shape, thereby forming a filter body 102. Then, both corrugated ends of the filter body 102 are adhered to side sheets 104 and the filter body 102 is maintained in a predetermined shape, thereby completing the filter 100.
In the above production method of the filter 100, however, the activated carbon is sandwiched between the two sheets of nonwoven fabric and then the sheets of nonwoven fabric are press-formed into the corrugated shape to form the filter body 102. Therefore, when the sheets of nonwoven fabric are press-formed, it is necessary to prevent the activated carbon from falling out as well as to prevent the nonwoven fabric from being torn. Thus, there is a problem that much labor is required for forming the filter 100, thereby increasing the production cost.
It is an object of the invention to improve the forming efficiency when a filter medium is produced, as well as to reduce the production cost of the filter medium.
According to a first aspect of the invention, there is provided a production method of a filter medium comprising the steps of: preparing a first fiber layer formed into the same shape as that of one side surface of the filter medium; disposing a function member on a surface of the first fiber layer; and forming a second fiber layer by spinning partially melted fibers on the function member disposed on the surface of the first fiber layer.
According to the first aspect, the filter medium can be formed by laminating the function member and the second fiber layer in this order on the first fiber layer which is formed in a shape identical to that of one side surface of the filter medium. Thus, it is unnecessary to carry out press-forming in a state in which the function member is sandwiched between nonwoven fabrics. Therefore, a countermeasure to prevent the filter medium from falling out and a countermeasure to prevent the nonwoven fabric from being torn by the filter medium are unnecessary. Therefore, the forming efficiency when the filter medium is formed is improved and the production cost of the filter medium can be reduced.
Here, the function member may include various members such as a member having a function of absorbing fuel vapor, a member having a moisture absorbing function, a member having a deodorant function, and a member having a function of reinforcing the filter medium.
In the above aspect, the partially melted fibers can be spun to a die surface to form the first fiber layer. This facilitates the forming of the first fiber layer.
In the above aspect, a recess of a bag-like portion provided in a filter portion of the first fiber layer can be filled with the function member. With this, even if the recess tries to deform by negative pressure of fluid flowing through the bag-like portion, the deformation is suppressed by the function member filled in the recess. Therefore, it is possible to prevent the ventilation resistance of the filter medium from being increased.
In the above aspect, the function member may be disposed inward of an edge of the first fiber layer, and the second fiber layer may be laminated on this function member and the first fiber layer. By doing this, the function member is sealed by the joined portion between the edge of the first fiber layer and the edge of the second fiber layer. Thus, the function member does not fall out from between the first fiber layer and the second fiber layer irrespective of whether the function member
In the above aspect, in a state in which the second fiber layer has plasticity, superposed edges of the first fiber layer and the second fiber layer can be pressed together. By doing this, the edge of the first fiber layer and the edge of the second fiber layer can be joined to each other strongly and the sealing strength of the edge of the filter medium is enhanced. Further, since the edge is cured into a plate-like shape, the edge becomes a support flange for the filter medium and the rigidity of the entire filter medium is enhanced.
In the above aspect, the function member may be disposed such that an edge thereof is located outward of an edge of the first fiber layer. This enables a support flange to be formed by the function member on the edge of the filter medium.
According to a second aspect of the invention, the filter medium comprises a first fiber layer formed in a shape identical to that of one side surface of the filter medium and having a filter portion including a bag-like portion; a function member filled in the bag-like portion of the first fiber layer; and a second fiber layer disposed on a surface of the function member. Therefore, it is unnecessary to carry out press-forming in a state in which the function member is sandwiched between the nonwoven fabrics, the forming efficiency when the filter medium is formed is improved, and the production cost of the filter medium can be reduced. Further, even if the recess tries to deform in a contractive direction by negative pressure of fluid passing through the bag-like portion, the deformation is suppressed by the function member filled in the recess.